1. Field of the Invention
The invention concerns the field of reaction injection molded polyurethanes.
2. Description of the Prior Art
Reaction Injection Molding (RIM) is a technique for the rapid mixing and molding of large, fast curing urethane parts. RIM polyurethane parts are used in a variety of exterior body applications on automobiles where their light weight contributes to energy conservation. RIM parts are generally made by rapidly mixing active hydrogen containing materials with polyisocyanate and placing the mixture into a mold where reaction proceeds. These active hydrogen containing materials comprise a high molecular weight polyhydric polyether and a low molecular weight active hydrogen containing compound. After reaction and demolding, the parts may be subjected to an additional curing step which comprises placing the parts in an ambient temperature of about 250.degree. F. or greater.
In a previously filed patent application, Ser. No. 136,199 filed April 1, 1980, now U.S. Pat. No. 4,273,885, a catalyst system for RIM polyurethane elastomers was described which was comprised of dimorpholinodiethylether, dibutyltin dilaurate and an alkyltin mercaptide. The catalyst combination in that patent application imparts superior processing characteristics to RIM polyurethane elastomer systems. However, we have since discovered that the use of dimorpholinodiethylether, while advantageous in many RIM systems, interferes in the cure of certain important paint systems known as high solids enamel paints. We have discovered that by substituting a reactive amine catalyst, which is tied up in the polymer network by reaction, for dimorpholinodiethylether that the processing benefits already described in the above mentioned patent application are retained and the RIM part can be painted using the high solids enamel paint systems. The reactive amine catalyst used in our present invention is methyldiethanolamine.